Process for the production of copolycarbonates with reduced color

ABSTRACT

A method is provided for reducing the color generated during production of copolycarbonate that includes quinone-type residues. The method includes the steps of mixing the precursors of monomer residues, a carbonate source and a polymerization catalyst into a reaction mixture. The method further includes the steps of introducing an antioxidant such as a hydroxycarboxylic acid to the reaction mixture in an amount sufficient to reduce color formation and introducing the reaction mixture to a series of process units wherein the reaction mixture polymerizes. The resulting copolycarbonate has improved color as compared to a copolycarbonate formed in a process without the step of introducing an antioxidant to the melt polymerization process.

RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application No.60/540,414 filed on Jan. 29,2004, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

Polycarbonate is a thermoplastic that has excellent mechanicalproperties such as impact resistance, heat resistance and transparency.Polycarbonates are widely used in applications ranging from footballhelmets to automobile parts to transparent security windows. Morerecently, polycarbonates have also proven to be the material of choicefor optical media applications such as optical discs, for examplecompact discs (CD) and digital versatile discs (DVD). Conventionalpolycarbonates are usually produced by (1) an interfacialpolymerization, in which bisphenol A (BPA) is reacted directly withphosgene or (2) a melt polymerization process in which BPA istransesterified with a carbonic acid diester such as diphenyl carbonate(DPC). For many applications, there has been a need for materialspossessing the fundamental characteristics of transparency and toughnessinherent in BPA polycarbonate but possessing, in addition, certainimprovements in physical properties relative those possessed bybisphenol A polycarbonate (BPA-PC), for example reduced birefringencefor optical applications. For some applications improved chemicalresistance relative to BPA polycarbonate is required, for example incertain medical and automotive applications. Copolycarbonates arematerials frequently possessing the fundamental traits of BPApolycarbonate, transparency and toughness, but in certain instances alsopossessing improved performance characteristics for a given applicationrelative to BPA polycarbonate.

One example of such a copolycarbonate comprises repeat units derivedfrom resorcinol or hydroquinone in addition to repeat units derived frombisphenol A. The incorporation of resorcinol-derived andhydroquinone-derived repeat units into a BPA-polycarbonate confersexcellent melt flow properties, molding properties, solvent and heatresistance, while maintaining the excellent mechanical properties andtransparency inherent in bisphenol A polycarbonate. Suchcopolycarbonates can be prepared by interfacial polymerization, meltpolymerization, or solid state polymerization. (U.S. Pat. No.6,177,536). The present invention relates to an improved method toprepare these and related copolycarbonates using the melt polymerizationmethod.

SUMMARY OF THE INVENTION

Applicants have determined that the formation of color in quinone-likecopolycarbonates can be reduced by adding an antioxidant to the meltpolymerization process. Thus, an embodiment of the present inventionprovides a method of producing a copolycarbonate with improved colorwherein the method comprises the steps of,

i. preparing a molten reaction mixture comprising a first dihydroxyaromatic compound comprising monomer residue (a), a second dihydroxyaromatic compound comprising monomer residue (b), a carbonate source,and a polymerization catalyst,

-   -   wherein monomer residue (a) is a quinone structure or a        structure capable of forming a quinone structure upon oxidation,    -   wherein monomer residue (b) is a quinone structure or a        structure capable of forming a quinone structure upon oxidation        different from monomer residue (a), or is,        -   where B is    -   —O—, —CO—, —S—, —SO₂—, a C₆-C₂₀ aromatic radical, or a C₆-C₂₀        cycloaliphatic radical; the groups R¹ and R² are independently a        hydrogen atom, C₁-C₂₀ alkyl radical, C₄-C₂₀ cycloalkyl radical,        or C₄-C₂₀ aryl radical; or R¹ and R² together form a C₄-C₂₀        cycloaliphatic ring which is optionally substituted by one or        more C₁-C₂₀ alkyl, C₆-C₂₀ aryl, C₅-C₂₁ aralkyl, C₅-C₂₀        cycloalkyl groups or a combination thereof, R³ is a divalent        hydrocarbylene group, and R⁴ and R⁵ are independently a hydrogen        atom, halogen atom, nitro group, cyano group, C₁-C₂₀ alkyl        radical C₄-C₂₀ cycloalkyl radical, or C₆-C₂₀ aryl radical and p        and q are both integers from 0 to 4,

ii. introducing an antioxidant such as a hydroxycarboxylic acid to thereaction mixture in an amount sufficient to result in a productcopolycarbonate with improved color,

iii. introducing the reaction mixture to a series of process units, and

iv. allowing the reaction mixture to polymerize thereby formingcopolycarbonate, wherein the copolycarbonate has improved color ascompared to a copolycarbonate formed in a melt process without theintroduction of antioxidant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an embodiment of a melt polymerization processof the current invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood more readily by reference to thefollowing detailed description of preferred embodiments of the inventionand the examples included therein. The present invention provides amethod for improving the color of a copolycarbonate produced by meltpolymerization wherein the copolycarbonate comprises monomer residues ofdihydroxy aromatic compounds and diaryl carbonates. The method comprisesthe steps of;

i. preparing a molten reaction mixture comprising a first dihydroxyaromatic compound comprising monomer residue (a), a second dihydroxyaromatic compound comprising monomer residue (b), a carbonate source,and a polymerization catalyst,

-   -   wherein monomer residue (a) is a quinone structure or a        structure capable of forming a quinone structure upon oxidation,    -   wherein monomer residue (b) is a quinone structure or a        structure capable of forming a quinone structure upon oxidation        different from monomer residue (a), or is,        -   where B is    -   —O—, —CO—, —S—, —SO₂—, a C₆-C₂₀ aromatic radical, or a C₆-C₂₀        cycloaliphatic radical; the groups R¹ and R² are independently a        hydrogen atom, C₁-C₂₀ alkyl radical, C₄-C₂₀ cycloalkyl radical,        or C₄-C₂₀ aryl radical; or R¹ and R² together form a C₄-C₂₀        cycloaliphatic ring which is optionally substituted by one or        more C₁-C₂₀ alkyl, C₆-C₂₀ aryl, C₅-C₂₁, aralkyl, C₅-C₂₀        cycloalkyl groups or a combination thereof, R³ is a divalent        hydrocarbylene group, and R⁴ and R⁵ are independently a hydrogen        atom, halogen atom, nitro group, cyano group, C₁-C₂₀ alkyl        radical C₄-C₂₀ cycloalkyl radical, or C₆-C₂₀ aryl radical and p        and q are both integers from 0 to 4,

ii. introducing an antioxidant such as a hydroxycarboxylic acid to thereaction mixture in an amount sufficient to result in a productcopolycarbonate with improved color,

iii. introducing the reaction mixture to a series of process units; and

iv. allowing the reaction mixture to polymerize thereby formingcopolycarbonate, wherein the copolycarbonate has improved color ascompared to a copolycarbonate formed in a melt process without theintroduction of antioxidant.

In the specification and the claims which follow, reference will be madeto a number of terms which shall be defined to have the followingmeanings:

The singular forms “a”, “an” and “the” include plural referents unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

“Copolycarbonate” refers to polycarbonates incorporating repeat unitsderived from at least two dihydroxy aromatic compounds and includescopolyestercarbonates, for example a polycarbonate comprising repeatunits derived from resorcinol, bisphenol A, and dodecandioic acid.Nothing in the description and claims of this application should betaken as limiting the copolycarbonate to only two dihydroxy aromaticresidues unless the context is expressly limiting. Thus, the applicationencompasses copolycarbonates with residues of 2, 3, 4, or more types ofdihydroxy aromatics.

“BPA” is herein defined as bisphenol A or2,2-bis(4-hydroxyphenyl)propane.

“Substantial polymerization” is where the average molecular weight(M_(w)) of the copolycarbonate is less than 5,000 (PS standards).

“Melt polycarbonate” refers to a polycarbonate made by thetransesterification of a diarylcarbonate with a dihydroxy aromaticcompound.

“Catalyst system” as used herein refers to a catalyst or catalysts thatcatalyze the transesterification of a dihydroxy aromatic compound with adiarylcarbonate in the preparation of melt polycarbonate.

“Catalytically effective amount” refers to an amount of a catalyst atwhich catalytic performance is exhibited.

“Monomer mix tank” refers to the area of the process wherein thereaction mixture is prepared. The word tank does not limit the inventionto the mixing of monomers within a single vessel. The mixing may occurin a series of tanks or by any other means to prepare a mixture.

“Process units” refers to the area within the system wherein themonomers react and where copolycarbonate weight is built. This may occurwithin, among other places, extruders, equilibration vessels,continuously stirred tank reactors, batch reactors, packed bed reactorsor heat exchangers.

“Plaque Yellowness Index” refers to a measurement of color of a sampleof copolycarbonate using a UV spectrophotometer converted to a 1 mmthick sample value. It is preferable that the copolycarbonate made bythe method of the present invention have a plaque yellowness index valueof between 0.4 and 8.0, more preferably between 0.04 and 5.0 and stillmore preferably between 0.04 and 3.0. The plaque YI of the resultingcopolycarbonate is affected by the initial quality of the quinone typestructure.

“Solution Yellowness Index” refers to the yellowness of the reactionmixture prior to substantial polymerization. Data can be measured with aUV/VIS spectrophotometer on a 10% Copolymer solution in MECl₂. Thetransmission can be measured on 3 wavelengths (445 NM, 555 NM, and 600NM) against a MeCl₂ blank. With the following calculation the sol YI canbe calculated; (Sol YI=(% T600—% T445)/% T555*100%).

“Dihydroxy aromatic compound(s)” means an aromatic compound whichcomprises two hydroxy groups on one or more aromatic rings, for examplea bisphenol such as bisphenol A or a dihydroxy benzene such asresorcinol.

Numerical values in the specification and claims of this application,particularly as they relate to polymer compositions, reflect averagevalues for a composition that may contain individual polymers ofdifferent characteristics. Furthermore, the numerical values should beunderstood to include numerical values which are the same when reducedto the same number of significant figures and numerical values whichdiffer from the stated value by less than the experimental error of themeasurement technique used in the present application to determine thevalue.

The present invention provides a method for preparing a copolycarbonate.An embodiment of the method comprises contacting under meltpolymerization conditions a first dihydroxy aromatic compound containingthe precursor of monomer residue (a), and at least one second dihydroxyaromatic compound containing the precursor of monomer residue (b), withat least one diarylcarbonate containing the precursor of monomer residue(c), an antioxidant and at least one melt polymerization catalyst.

The First Dihydroxy Aromatic Compound:

The first dihydroxy aromatic compound comprises monomer residue (a). Itcan be any quinone structure or structure capable of forming a quinonestructure upon oxidation. Suitable types of these dihydroxy aromaticcompounds may be selected from the group consisting of dihydroxybenzenes having structure I

where each R¹⁰ is independently at each occurrence a hydrogen atom,halogen atom, nitro group, cyano group, C₁-C₂₀ alkyl, C₄-C₂₀ cycloalkylradical, C₄-C₂₀ aryl radical, and n is an integer from 0 to 4.

Non-limiting examples of dihydroxy benzenes having structure I areresorcinol; hydroquinone; 4-methylresorcinol; 5-methylresorcinol;2-methylhydroquinone; 2-ethylhydroquinone; 2,5-dimethylhydroquinone;2,6-dimethylhydroquinone; catechol; 3-methylcatechol; 4-methylcatechol;butylhydroquinone; and mixtures thereof.

The Second Dihydroxy Aromatic Compound:

The second dihydroxy aromatic compound forms the precursor of monomerresidue (b) such that the polymer formed is a copolycarbonate. It can beany quinone structure or structure capable of forming a quinonestructure upon oxidation different from monomer residue (a) such thatthe polymer formed is a copolycarbonate. Suitable types of thesedihydroxy aromatic compounds again may be selected from the groupconsisting of dihydroxy benzenes having structure I

where each R¹⁰ is as defined as above and non non-limiting examples ofsuch are as defined above.

Alternatively the second dihydroxy aromatic compound may be a bisphenolhaving structure II

where B is,

—O—, —CO—, —S—, —SO₂—, a C₆-C₂₀ aromatic radical, or a C₆-C₂₀cycloaliphatic radical; the groups R¹ and R² are independently ahydrogen atom, C₁-C₂₀ alkyl radical, C₄-C₂₀ cycloalkyl radical, orC₄-C₂₀ aryl radical; or R¹ and R² together form a C₄-C₂₀ cycloaliphaticring which is optionally substituted by one or more C₁-C₂₀ alkyl, C₆-C₂₀aryl, C₅₁-C₂, aralkyl, C₁-C₂₀ cycloalkyl groups or a combinationthereof, R³ is a divalent hydrocarbylene group, and R⁴ and R⁵ areindependently a hydrogen atom, halogen atom, nitro group, cyano group,C₁-C₂₀ alkyl radical C₄-C₂₀ cycloalkyl radical, or C₆-C₂₀ aryl radicaland p and q are both integers from 0 to 4.

Bisphenols having structure II are illustrated by2,2-bis(4-hydroxyphenyl)propane (bisphenol A);2,2-bis(3-chloro-4-hydroxyphenyl)propane;2,2-bis(3-bromo-4-hydroxyphenyl)propane;2,2-bis(4-hydroxy-3-methylphenyl)propane;2,2-bis(4-hydroxy-3-isopropylphenyl)propane;2,2-bis(3-t-butyl-4-hydroxyphenyl)propane;2,2-bis(3-phenyl-4-hydroxyphenyl)propane;2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane;2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane; 2,2-bis(3,5-dimethyl-4-hydroxyphenyl )propane;2,2-bis(3-chloro-4-hydroxy-5-methylphenyl)propane; 2,2-bis(3-bromo-4-hydroxy-5-methylphenyl)propane;2,2-bis(3-chloro-4-hydroxy-5-isopropylphenyl)propane;2,2-bis(3-bromo-4-hydroxy-5-isopropylphenyl)propane;2,2-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)propane;2,2-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)propane;2,2-bis(3-chloro-5-phenyl-4-hydroxyphenyl)propane;2,2-bis(3-bromo-5-phenyl-4-hydroxyphenyl)propane;2,2-bis(3,5-disopropyl-4-hydroxyphenyl)propane;2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane;2,2-bis(3,5-diphenyl-4-hydroxyphenyl)propane;2,2-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)propane;2,2-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)propane;2,2-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)propane;2,2-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)propane;2,2-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)propane;1,1-bis(4-hydroxyphenyl)cyclohexane;1,1-bis(3-chloro-4-hydroxyphenyl)cyclohexane;1,1-bis(3-bromo-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane;1,1-bis(4-hydroxy-3-isopropylphenyl)cyclohexane;1,1-bis(3-t-butyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-phenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-dichloro-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-dibromo-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-chloro-4-hydroxy-5-methylphenyl)cyclohexane;1,1-bis(3-bromo-4-hydroxy-5-methylphenyl)cyclohexane;1,1-bis(3-chloro-4-hydroxy-5-isopropylphenyl)cyclohexane;1,1-bis(3-bromo-4-hydroxy-5-isopropylphenyl)cyclohexane;1,1-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)cyclohexane;1,1-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-chloro-5-phenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-bromo-5-phenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-disopropyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-di-t-butyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-diphenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)cyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)cyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)cyclohexane;1,1-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)cyclohexane;1,1-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-chloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-3-methylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-3-isopropylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-dichloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-dibromo-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-chloro-4-hydroxy-5-methylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-4-hydroxy-5-methylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-chloro-4-hydroxy-5-isopropylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-4-hydroxy-5-isopropylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;bis(3-chloro-5-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-5-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-disopropyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-di-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-diphenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;4,4′dihydroxy-1,1-biphenyl; 4,4′-dihydroxy-3,3′-dimethyl-1,1-biphenyl;4,4′-dihydroxy-3,3′-dioctyl-1,1-biphenyl; 4,4′-dihydroxydiphenylether;4,4′-dihydroxydiphenylthioether;1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene;1,3-bis(2-(4-hydroxy-3-methylphenyl)-2-propyl)benzene;1,4-bis(2-(4-hydroxyphenyl)-2-propyl)benzene; and1,4-bis(2-(4-hydroxy-3-methylphenyl)-2-propyl)benzene. In manyapplications due to its relatively high reactivity, thermal stability,and low cost, bisphenol A (BPA) is frequently preferred.

The Carbonate Source:

In the production of copolymerized polycarbonates in accordance with thepresent invention, the compounds which react with the dihydroxycompounds to form carbonate linkages (the carbonate source) may becarbonate diesters, carbonyl halides, etc. Specific examples include:diphenyl carbonate, ditolyl carbonate, bis(chlorophenyl) carbonate,m-cresyl carbonate dinaphthyl carbonate, bis(diphenyl)carbonate, diethylcarbonate, dimethyl carbonate, dibutyl carbonate, dicyclohexylcarbonate, and other carbonate diesters, phosgene, and other carbonylhalides. Of the various compounds of this type, diphenyl carbonate isoften preferred.

The carbonate can be also be derived from an activated dicarbonate or amixture of an activated carbonate with diphenyl carbonate. A preferredactivated carbonate of the present invention is an activateddiarylcarbonate such as bismethylsalicylcarbonate (BMSC). However, asused herein the term “activated carbonate” is defined as adiarylcarbonate which is more reactive than diphenylcarbonate towardtransesterification reactions. Such activated carbonates are of thegeneral formula:

wherein Ar is a substituted aromatic radical having 6 to 30 carbonatoms. The preferred activated carbonates have the more specific generalformula:

wherein Q and Q′ are each independently activating groups. A and A′ areeach independently aromatic rings which can be the same or differentdepending on the number and location of their substituent groups, and nor n′ are whole numbers of zero up to a maximum equivalent to the numberof replaceable hydrogen groups substituted on the aromatic rings A andA′, wherein A+A′ is greater than or equal to 1. R and R′ are eachindependently substituent groups such as alkyl, substituted alkyl,cycloalkyl, alkoxy, aryl, alkylaryl, cyano, nitro, halogen, andcarboalkoxy. The number of R groups is a whole number and can be 0 up toa maximum equivalent to the number of replaceable hydrogen groups on thearomatic rings A minus the number n. The number of R′ groups is a wholenumber and can be 0 up to a maximum equivalent to the number ofreplaceable hydrogen groups on the aromatic rings A minus the number n′.The number, type, and location of the R and R′ substituents on thearomatic ring are not limited unless they deactivate the carbonate andlead to a carbonate which is less reactive than diphenylcarbonate.

Non-limiting examples of activating groups Q and Q′ are: alkoxycarbonylgroups, halogens, nitro groups, amide groups, sulfone groups, sulfoxidegroups, or imine groups with structures indicated below:

Specific and non-limiting examples of activated carbonates includebis(o-methoxycarbonylphenyl)carbonate, bis(o-chlorophenyl)carbonate,bis(o-nitrophenyl)carbonate, bis(o-acetylphenyl)carbonate,bis(o-phenylketonephenyl)carbonate, bis(o-formylphenyl)carbonate.Unsymmetrical combinations of these structures, where the substitutionnumber and type on A and A′ are different, are also possible to employin the current invention. A preferred structure for an activatedcarbonate is an ester-substituted diarylcarbonate having the structure:

wherein R¹ is independently at each occurrence a C¹-C₂₀ alkyl radical,C₄-C₂₀ cycloalkyl radical, or C₄-C₂₀ aromatic radical; R² isindependently at each occurrence a halogen atom, cyano group, nitrogroup, C₁-C₂₀ alkyl radical, C₄-C₂₀ cycloalkyl radical, C₄-C₂₀ aromaticradical, C₁-C₂₀ alkoxy radical, C₄-C₂₀ cycloalkoxy radical, C₄-C₂₀aryloxy radical, C₁-C₂₀ alkylthio radical, C₄-C₂₀ cycloalkylthioradical, C₄-C₂₀ arylthio radical, C₁-C₂₀ alkylsulfinyl radical, C₄-C₂₀cycloalkylsulfonyl radical, C₄-C₂₀ arylsulfinyl radical, C₁-C₂₀alkylsulfonyl radical, C₄-C₂₀ cycloalkylsulfonyl radical, C₄-C₂₀arylsulfonyl radical, C₁-C₂₀ alkoxycarbonyl radical, C₄-C₂₀cycloalkoxycarbonyl radical, C₄-C₂₀ aryloxycarbonyl radical, C₂-C₆₀alkylamino radical, C₆-C₆₀ cycloalkylamino radical, C₅-C₆₀ arylaminoradical, C₁-C₄₀ alkylaminocarbonyl radical, C₄-C₄₀cycloalkylaminocarbonyl radical, C₄-C₄₀ arylaminocarbonyl radical, orC₁-C₂₀ acylamino radical; and b is independently at each occurrence aninteger 0-4. At least one of the substituents CO₂R¹ is preferablyattached in an ortho position relative to the carbonate group.

Examples of preferred ester-substituted diarylcarbonates include but arenot limited to bis(methylsalicyl)carbonate (CAS Registry No.82091-12-1), bis(ethyl salicyl)carbonate, bis(propyl salicyl) carbonate,bis(butylsalicyl) carbonate, bis(benzyl salicyl)carbonate, bis(methyl4-chlorosalicyl)carbonate and the like. Typicallybis(methylsalicyl)carbonate is preferred for use in melt polycarbonatesynthesis due to its lower molecular weight and higher vapor pressure.

Some non-limiting examples of non-activating groups which, when presentin an ortho position relative to the carbonate group, would not beexpected to result in activated carbonates are alkyl, cycolalkyl orcyano groups. Some specific and non-limiting examples of non-activatedcarbonates are bis(o-methylphenyl)carbonate,bis(p-cumylphenyl)carbonate,bis(p-(1,1,3,3-tetramethyl)butylphenyl)carbonate andbis(o-cyanophenyl)carbonate. Unsymmetrical combinations of thesestructures are also expected to result in non-activated carbonates.

Unsymmetrical diarylcarbonates wherein one aryl group is activated andone aryl is unactivated or de-activated would also be useful in thisinvention if the activating group renders the diaryl carbonate stillmore reactive than diphenyl carbonate.

The carbonate may also be derived from dicarboxylic acids, dicarboxylicacid esters, or dicarboxylic acid halides. Such constituent repeatingunits are typically polyester-polycarbonate units. Non-limiting examplesof dicarboxylic acids include terephthalic acid, isophthalic acid,sebacic acid, decanedioic acid, dodecanedioic acid, etc. Non-limitingexamples of dicarboxylic acid esters include diphenyl sebacate, diphenylterephthalate, diphenyl isophthalate, diphenyl decanedioate, diphenyldodecanedioate, etc. Non-limiting examples of dicarboxylic acid halidesinclude terephthaloyl chloride, isophthaloyl chloride, sebacoylchloride, decanedioyl chloride, dodecanedioyl chloride, etc. Suchpolyester-polycarbonate units may be present in proportions of up to 50mole %, preferably not more than 30 mole %, in copolymerizedpolycarbonates in accordance with the present invention.

The Catalyst:

The method of the invention also comprises the step of introducing acatalyst to the reaction mixture to initiate a polymerization reaction.The catalyst may be introduced continuously, or may be introducedbatchwise and may occur before, during or after the introduction of theprecursors of monomer residues (a) or (b), or the carbonate.

The catalyst used in the method of the present invention is a base, andpreferably comprises at least one source of alkaline earth ions oralkali metal ions, and/or at least one quaternary ammonium compound, aquaternary phosphonium compound or a mixture thereof. The source ofalkaline earth ions or alkali metal ions being used in an amount suchthat the amount of alkaline earth or alkali metal ions present in thereaction mixture is in a range between 10⁻⁵ and 10⁻⁸ moles alkalineearth or alkali metal ion per mole of dihydroxy aromatic compoundemployed.

The quaternary ammonium compound is selected from the group of organicammonium compounds having structure III,

wherein R²⁰-R²³ are independently a C₁-C₂₀ alkyl radical, C₄-C₂₀cycloalkyl radical, or a C₄-C₂₀ aryl radical; and X⁻ is an organic orinorganic anion. In one embodiment of the present invention anion X⁻ isselected from the group consisting of hydroxide, halide, carboxylate,sulfonate, sulfate, formate, carbonate, and bicarbonate.

Non-limiting examples of suitable organic ammonium compounds comprisingstructure III are tetramethyl ammonium hydroxide, tetrabutyl ammoniumhydroxide, tetramethyl ammonium acetate, tetramethyl ammonium formateand tetrabutyl ammonium acetate. Tetramethyl ammonium hydroxide is oftenpreferred.

The quaternary phosphonium compound is selected from the group oforganic phosphonium compounds having structure IV,

wherein R²⁴-R²⁷ are independently a C¹-C²⁰ alkyl radical, C⁴-C²⁰cycloalkyl radical, or a C₄-C₂₀ aryl radical; and X⁻ is an organic orinorganic anion. In one embodiment of the present invention anion X⁻ isan anion selected from the group consisting of hydroxide, halide,carboxylate, sulfonate, sulfate, formate, carbonate, and bicarbonate.Suitable organic phosphonium compounds comprising structure TV areillustrated by tetramethyl phosphonium hydroxide, tetramethylphosphonium acetate, tetramethyl phosphonium formate, tetrabutylphosphonium hydroxide, and tetrabutyl phosphonium acetate (TBPA). TBPAis often preferred.

Where X⁻ is a polyvalent anion such as carbonate or sulfate it isunderstood that the positive and negative charges in structures III andIV are properly balanced. For example, where R²⁰-R²³ in structure IIIare each methyl groups and X⁻ is carbonate, it is understood that X⁻represents ½ (CO₃ ⁻²).

Suitable sources of alkaline earth ions include alkaline earthhydroxides such as magnesium hydroxide and calcium hydroxide. Suitablesources of alkali metal ions include the alkali metal hydroxidesillustrated by lithium hydroxide, sodium hydroxide and potassiumhydroxide. Other sources of alkaline earth and alkali metal ions includesalts of carboxylic acids, such as sodium acetate and derivatives ofethylene diamine tetraacetic acid (EDTA) such as EDTA tetrasodium salt,and EDTA magnesium disodium salt. Sodium hydroxide is often preferred.

In order to achieve the formation of copolycarbonate using the method ofthe present invention an effective amount of catalyst must be employed.The amount of catalyst employed is typically based upon the total numberof moles of first dihydroxy aromatic compound and second dihydroxyaromatic compound employed in the polymerization reaction. Whenreferring to the ratio of catalyst, for example phosphonium salt IV, toall dihydroxy aromatic compounds employed in the polymerizationreaction, it is convenient to refer to moles of phosphonium salt permole of the first and second dihydroxy aromatic compounds combined,meaning the number of moles of phosphonium salt divided by the sum ofthe moles of each individual dihydroxy aromatic compound present in thereaction mixture. The amount of organic ammonium or phosphonium saltsIII or IV employed typically will be in a range between 1×10⁻² and1×10⁻⁵, preferably between 1×10⁻³ and 1×10⁻⁴ moles per mole of the firstand second dihydroxy aromatic compounds combined. The inorganic metalhydroxide catalyst typically will be used in an amount corresponding tobetween 1×10⁻⁴ and 1×10⁻⁸, preferably 1×10⁻⁴ and 1×10⁻⁷ moles of metalhydroxide per mole of the first and second dihydroxy aromatic compoundscombined.

The Antioxidant:

Several types of antioxidants may be used in accordance with the presentinvention. Exemplary of antioxidants that may be used in accordance withthe present invention are hydroxycarboxylic acids, benzofuranones,phenolic antioxidants including sterically hindered phenols,hydroxylamines including dialkylhydroxylamines, functionalized aliphatichydroxylamines, or substituted dibenzylhydroxylamine.

Non-limiting examples of hydroxycarboxylic acids that may be usedinclude tartaric acid, maleic acid, lactic acid, tartronic acid andesters of these acids. It is yet another aspect of the present inventionthat the salts of the aforementioned acids be used.

An effective amount of antioxidant should be introduced to the reactionmixture in order to ensure a copolycarbonate product with improvedcolor. An excessive amount may have the effect of degrading the catalystused in the reaction. Thus in certain embodiments, an effective amountof hydroxycarboxylic acid is less than 10 ppm, more preferably less than5 ppm, and still more preferably less than 1 ppm based on the weight ofthe precursor of monomer residue (a) in the molten reaction mixture.

The Melt Process:

The term “contacting under melt polymerization conditions” will beunderstood to mean those conditions necessary to effect reaction betweenthe diarylcarbonate and the dihydroxy aromatic compounds employedaccording to the method of the present invention. The reactiontemperature is typically in the range between 150° C. and 350° C., morepreferably between 180° C. and 310° C. The pressure may be atatmospheric pressure, supra atmospheric pressure, or a range ofpressures, for example from 2 atmospheres to 15 torr in the initialstages of the polymerization reaction, and at a reduced pressure atlater stages, for example in a range between 15 torr and 0.1 torr. Thereaction time is generally in a range between 0.1 hours and 10 hours,preferably between 0.1 and 5 hours.

FIG. 1 illustrates a melt process according to an embodiment of thepresent invention. The first stage of the process is to mix the firstand second dihydroxy aromatic compounds, comprising the precursors ofmonomer residues (a) and (b), with the carbonate compound, therebyforming a reaction mixture. An antioxidant is introduced to the reactionmixture either during its preparation or after the mixture has beenprepared. The reaction mixture is then fed to a series of processequipment wherein a copolymerization reaction takes place and molecularweight of the resulting copolycarbonate is increased.

In one embodiment of the present invention, at least one first dihydroxyaromatic compound comprising the precursor of monomer residue (a) and atleast one second dihydroxy aromatic compound comprising the precursor ofmonomer residue (b) are employed in amounts such that the molar ratio ofthe first dihydroxy aromatic compound to the second dihydroxy aromaticcompound is in a range between 0.01 and 99.00. Where the seconddihydroxy aromatic compound comprises two or more compounds, for examplea mixture of resorcinol and hydroquinone, and the first dihydroxycompound is a single compound, for example BPA, the molar ratio of thefirst dihydroxy aromatic compound to the second dihydroxy aromaticcompound is expressed as the sum of the number of moles of resorcinoland hydroquinone used divided by the number of moles of BPA used.Similarly, where the second dihydroxy aromatic compound comprises but asingle compound, for example resorcinol, and the first dihydroxyaromatic compound comprises a mixture of compounds, for example, BPA andBPZ (1,1-bis(4-hydroxyphenyl)cyclohexane), the molar ratio of the seconddihydroxy aromatic compound to the first dihydroxy aromatic compound isexpressed as the number of moles of resorcinol used divided by the sumof the number of moles of BPA and BPZ used. As mentioned, in oneembodiment the molar ratio of the second dihydroxy aromatic compound tothe first dihydroxy aromatic compound is in a range between 0.01 and 99.In an alternate embodiment the molar ratio of the second dihydroxyaromatic compound to the first dihydroxy aromatic compound is in a rangebetween 0.05 and 0.7. A copolycarbonate prepared according to the methodof the present invention using resorcinol as the second dihydroxyaromatic compound and BPA as the first dihydroxy aromatic compound inwhich the molar ratio of resorcinol to BPA was 0.7 could contain as muchas 41 mole percent resorcinol derived repeat units if no loss occurredduring the polymerization reaction.

Typically, the method of the present invention is carried out such thatthe amount of diarylcarbonate employed corresponds to a molar ratio ofdiarylcarbonate to all dihydroxy aromatic compounds, i.e. the firstand/or second dihydroxy aromatic compounds, initially present in thereaction mixture, the molar ratio being in a range between 0.90 and1.20, preferably between 1.01 and 1.10.

The method of the present invention further comprises the step ofintroducing an antioxidant to the reaction mixture. The introduction ofthe antioxidant may take place at any one or a combination of placeswithin the polymerization process. As illustrated in FIG. 1, anembodiment of the melt process of the present invention includes severalbasic stages. The first stage is to mix the precursors of monomerresidues (a), monomer residues (b), a carbonate source and apolymerization catalyst into a reaction mixture. The reaction mixture isthen fed to a series of process equipment wherein polymerizationreactions occur thereby building polymer weight.

The antioxidant may be introduced to the reaction mixture prior to orduring the melting of monomer residues (a), monomer residues (b), or thecarbonate source may be introduced in a melter or a feed line to amelter. Further, the antioxidant may be introduced to the reactionmixture after melting monomer residues (a), monomer residues (b), andthe carbonate source. If so, it may be introduced to the molten reactionmixture in a melter, a feed line to a monomer mix tank, the monomer mixtank, a feed line from the monomer mix tank to a first process unit, thefirst process unit, a feed line to a second process unit, the secondprocess unit, a feed line to a third process unit, the third processunit, or combinations thereof. In order to prevent further undesirableoxidation reactions with the melt polymerization catalyst it is oftenpreferred that the introduction of the antioxidant occur prior to theintroduction of the polymerization catalyst.

Optional Catalyst Introduction Strategy

U.S. patent application Ser. No. 10/768,575, herein incorporated byreference, discloses and claims a method of reducing the color generatedduring the production of polycarbonates. In some embodiments, inaddition to the introduction of an antioxidant, the method of thepresent invention includes the steps of selecting a catalystintroduction strategy to reduce color formation and introducing thecatalysts to the reaction mixture in accordance with the selectedstrategy. As noted the catalyst introduction strategy incorporates theintroduction of an organic catalyst and an inorganic catalyst.

FIG. 1 shows a melt polymerization processes of the type that may beemployed with the current invention. Precursors of monomer residues (a)and (b), and a carbonate source are introduced to a monomer mix tankwhere they are mixed thereby forming a reaction mixture. The reactionmixture is then sent to a series of process units wherein polymerizationreactions occur and copolymer weight increases. The polymerizationcatalysts are added to the reaction mixture per a selected strategy. Thecatalyst introduction strategies of the present invention includeseveral potential introduction points of organic and/or inorganiccatalysts.

The polymerization catalysts introduction may occur in at least threeschemes. The first scheme is to introduce the polymerization catalyststo the reaction mixture after monomer (a), monomer (b) and the carbonatesource have been melted and prior to substantial polymerization of themonomers. The second strategy is to introduce the polymerizationcatalysts to the reaction mixture or precursors of one or more of themonomer residues prior to melting with the proviso that residence timeof the process from the start of melting until substantialpolymerization has occurred is less than 4 hours. The third strategy isto combine the first two strategies wherein the organic catalyst isintroduced to the reaction mixture prior to melting and the inorganiccatalyst is introduced after melting. The purpose of selecting thestrategy is so that the polymerization catalysts have minimal contactwith the reaction mixture so as to prevent an undesirable oxidationreaction which produces an undesirable color formation within theresulting copolycarbonate.

Strategy 1:

The method of the present invention comprises the strategy ofintroducing the polymerization catalysts to the reaction mixture aftermonomer residues (a), monomer residues (b), and carbonate source aremelted and prior to substantial polymerization. The organic andinorganic catalysts may be introduced to the reaction mixture eithertogether or at separate points.

The introduction of the organic catalyst may occur in a monomer mixtank, or in a feed line to a first process unit. The organic catalystmay be introduced to the reaction mixture as it is prepared if meltingis performed prior to combination of the components, and may beintroduced with the monomer residues or the carbonate source either inthe same feed lines or in a separate feed line.

The introduction of the inorganic catalyst typically occurs at the sametime or after the introduction of the organic catalyst. If theintroduction occurs at the same time, the catalysts may be introducedwithin the same feed or in separate feeds at any of the aforementionedpoints where the organic catalyst may be introduced. It is preferred,however, that the introduction of the catalyst solution to the moltenreaction occur subsequent to the introduction of the precursor ofmonomer residue (a).

If the introduction of the inorganic catalyst occurs a different pointthan the introduction of the organic catalyst then the organic catalystis desirably introduced to the molten reaction mixture prior to a firstprocess unit while the inorganic catalyst is introduced to the moltenreaction mixture at any one of various points prior to substantialpolymerization of the molten reaction mixture. The inorganic catalystmay be introduced in the feed line from the monomer mix tank to a firstprocess unit, or to the molten reaction mixture in the first processunit, or to the molten reaction mixture in a feed line to a secondprocess unit, or to the molten reaction mixture in the second processunit, or to the molten reaction mixture in a feed line to a thirdprocess unit, or to the third process unit itself.

Strategy 2:

The method of the present invention comprises the strategy ofintroducing a polymerization catalyst to the reaction mixture prior tomelting monomer residues (a), monomer residues (b), and carbonate sourcewith the proviso that residence time of the process from the start ofmelting until substantial polymerization has occurred is less than 4hours, more preferably 30 minutes or less, and most preferably 15minutes or less.

The organic and inorganic catalysts may be introduced to the reactionmixture either together or at separate points. The inorganic and organiccatalysts may be introduced to a monomer mix tank or a melter togetherwith monomer residues (a), together with monomer residues (b), togetherwith the carbonate source, in a separate feed or combinations thereof.

Strategy 3:

The method of the present invention comprises the strategy ofintroducing a polymerization catalyst to the reaction mixture whereinthe organic catalyst is introduced to a monomer mix tank or a meltertogether with monomer residue (a), together with monomer residue (b),together with the carbonate source, in a separate feed or combinationsthereof. The inorganic catalyst is then introduced to the moltenreaction mixture, prior to substantial polymerization, within a monomermix tank, a feed line from a monomer mix tank to a first process unit,the first process unit, a feed line to a second process unit, the secondprocess unit, a feed line to a third process unit, the third processunit, or combinations thereof.

An embodiment of the present invention further comprises the step ofintroducing a dihydric phenol or other monomer to the molten reactionmixture within the series of process units through late monomeraddition. This addition of dihydric phenol may occur within the first,second, third or subsequent process units or the feed lines therebetween. It is preferable that the antioxidant is introduced to thereaction mixture prior to the late monomer addition. However, it ispossible to add the acid with the monomer of the late monomer addition.

The method of the present invention may be employed to provide highmolecular weight copolycarbonates. High molecular weightcopolycarbonates are defined as copolycarbonates having a weight averagemolecular weight, M_(w), greater than 15,000 (PS standards). The methodof the present invention may also be employed to provide oligomericcopolycarbonates. Oligomeric copolycarbonates are defined ascopolycarbonates as having weight average molecular weight, M_(w), lessthan 15,000 (PS standards).

The invention also provides a method for making a molded article and amolded article formed from copolycarbonate with improved color preparedby the method including the steps of: preparing a molten reactionmixture comprising a first dihydroxy aromatic compound comprisingmonomer residue (a), a second dihydroxy aromatic compound comprisingmonomer residue (b), a carbonate source, and a polymerization catalyst;introducing an antioxidant such as a hydroxycarboxylic acid to thereaction mixture in an amount sufficient to result in a productcopolycarbonate with improved color; introducing the reaction mixture toa series of process units; allowing the reaction mixture to polymerizethereby forming copolycarbonate, wherein the copolycarbonate hasimproved color as compared to a copolycarbonate formed in a melt processwithout the introduction of antioxidant; and forming a molded articlefrom the copolycarbonate. The molded articles may be molded by interalia the processes of injection molding, blow molding, extrusion orcoextrusion.

Blends of copolymers are typical in industry. Thus the copolycarbonatesprepared using the method of the present invention may be blended withother polymeric materials, for example, other polycarbonates,polyestercarbonates, polyesters and olefin polymers such as ABS.Further, the copolycarbonates prepared using the method of the presentinvention may be blended with conventional additives such as heatstabilizers, mold release agents, and UV stabilizers. These blends maybe molded into various articles such as optical disks, optical lenses,automobile lamp components and the like. Thus, it is an aspect of thepresent invention to provide molded articles comprising the blends ofcopolycarbonate and/or the copolycarbonate produced by the method of thepresent invention.

EXAMPLES

Having described the invention in detail, the following examples areprovided. The examples should not be considered as limiting the scope ofthe invention, but merely as illustrative and representative thereof.The following measurements were made in these examples:

-   a.) Molecular weight: M_(w) and M_(n) were measured by GPC analysis    of 1 mg/ml polymer solutions in methylene chloride versus    polystyrene (PS) standards.-   b.) Solution Yellowness Index (YI) data was measured with a UV/VIS    spectrophotometer on a 10% Copolymer solution in MeCl₂. The    transmission was measured on 3 wavelengths (445 nm, 55 nm, and 600    nm) against a MeCl₂ blank. With the following calculation the sol YI    was calculated;    Sol YI=(% T600−% T445)/% T555*100%

c.) Small Scale Melt Polymerization reactions were carried out with BPAand additional monomer(s). See Examples 1 through 6 and Table 2. Thetotal amount of DPC (moles) equaled 1.08*(BPA+co-monomer/(total molesbisphenol)). The amount of DPC was held constant at 25 g in eachreaction. As catalysts, TMAH/(BPA+co-monomer)=2.5×10⁻⁴ (mole/mole) andNaOH (BPA+co-monomer)=1.5×10⁻⁶ (mole/mole) were added as an aqueoussolution (100 μl). Reactions were carried out by mixing aromaticdihydroxy compounds with DPC. After Nitrogen purging of the reactorsystem, polymerizations were carried out according to the reactionscheme illustrated in Table 1. TABLE 1 Reaction scheme for small scalemelt polymerizations. Reaction Stage Time (min) Temp (° C.) P (mbar) 1480 180 atm 2 60 230 170 3 30 270  20 4 30 300 0.5-1.5At the end of the reaction, the reactor was brought back to atmosphericpressure with a gentle nitrogen flow, and the polymer was harvested. Themelting time of 480 minutes was chosen to simulate plant conditions.

Example 1

In example 1, a batch reactor tube was charged under nitrogen with 19.73g of BPA, 2.38 g of resorcinol, 25.00 g of DPC, and 100 (μl) of anaqueous solution of TMAH and NaOH (2.5×10⁻⁴ and 1.5×10⁻⁶ molescatalyst/mole aromatic dihydroxy compound). Before the reaction, 1 ppm(relative to the amount of resorcinol) of tartaric acid was added to thereaction mixture as an aqueous solution of 100 (μl).

Example 2 (Comparative)

Example 1 was repeated without the addition of an antioxidant.

Example 3 (Comparative)

Example 2 was repeated except that the batch reactor tube was chargedunder nitrogen with 24.76 g of BPA, 25.00 g of DPC, and no resorcinol.

Example 4

Example 1 was repeated with 9 ppm (relative to the amount of resorcinol)of tartaric acid.

Example 5

Example 1 was repeated with (relative to the amount of resorcinol) of0.5 ppm tartaric acid.

Example 6

Example 1 was repeated with 1 ppm (relative to the amount of resorcinol)of tetrakismethylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)methane, CASReg. Number [6683-19-8]. TABLE 2 Experimental Results Example Mw(kg/mol) YI (Solution) 1 38.0 2.9  2* 56.0 8.2  3* 38.1 1.2 4 33.3 2.4 534.3 2.9 6 34.9 2.4*= Comparative

1. A method of producing a copolycarbonate with improved color whereinthe method comprises the steps of, i. preparing a molten reactionmixture comprising a first dihydroxy aromatic compound comprisingmonomer residue (a), a second dihydroxy aromatic compound comprisingmonomer residue (b), a carbonate source, and a polymerization catalyst,wherein monomer residue (a) is a quinone structure or a structurecapable of forming a quinone structure upon oxidation, wherein monomerresidue (b) is a quinone structure or a structure capable of forming aquinone structure upon oxidation different from monomer residue (a), oris,

where B is

—O—, —CO—, —S—, —SO₂—, a C₆-C₂₀ aromatic radical, or a C₆-C₂₀cycloaliphatic radical; the groups R¹ and R² are independently ahydrogen atom, C₁-C₂₀ alkyl radical, C₄-C₂₀ cycloalkyl radical, orC₄-C₂₀ aryl radical; or R¹ and R² together form a C₄-C₂₀ cycloaliphaticring which is optionally substituted by one or more C₁-C₂₀ alkyl, C₆-C₂₀aryl, C₅-C₂₁ aralkyl, C₅-C₂₀ cycloalkyl groups or a combination thereof,R³ is a divalent hydrocarbylene group, and R⁴ and R⁵ are independently ahydrogen atom, halogen atom, nitro group, cyano group, C₁-C₂₀ alkylradical C₄-C₂₀ cycloalkyl radical, or C₆-C₂₀ aryl radical and p and qare both integers from 0 to 4, ii. introducing an antioxidant such as ahydroxycarboxylic acid to the reaction mixture in an amount sufficientto result in a product copolycarbonate with improved color, iii.introducing the reaction mixture to a series of process units, and iv.allowing the reaction mixture to polymerize thereby formingcopolycarbonate, wherein the copolycarbonate has improved color ascompared to a copolycarbonate formed in a melt process without theintroduction of antioxidant.
 2. The method of claim 1, wherein theantioxidant is introduced to the reaction mixture prior to melting,during melting, or after melting monomer residues (a), monomer residues(b), the carbonate source or combinations thereof.
 3. The method ofclaim 2, wherein the antioxidant is introduced to the reaction mixtureprior to melting monomer residues (a), monomer residues (b), or thecarbonate source wherein the introduction of the antioxidant occurs in amelter or a feed line to a melter.
 4. The method of claim 2, wherein theantioxidant is introduced to the reaction mixture after melting monomerresidues (a), monomer residues (b), and the carbonate source wherein theintroduction of the antioxidant to the molten reaction mixture occurs ina melter, a feed line to a monomer mix tank, the monomer mix tank, afeed line from the monomer mix tank to a first process unit, the firstprocess unit, a feed line to a second process unit, the second processunit, a feed line to a third process unit, the third process unit, orcombinations thereof.
 5. The method of claim 2, wherein the wherein theantioxidant is introduced to the reaction mixture during the melting ofmonomer residues (a), monomer residues (b), or the carbonate sourcewherein the introduction of the antioxidant occurs in a melter or a feedline to a melter.
 6. The method of claim 2, wherein the antioxidant isintroduced in an amount of less than 10 ppm based on the weight of theprecursor of monomer residue (a) in the reaction mixture.
 7. The methodof claim 2, wherein the antioxidant is introduced in an amount of lessthan 5 ppm based on the weight of the precursor of monomer residue (a)in the reaction mixture.
 8. The method of claim 7, wherein theantioxidant is introduced in an amount of less than 1 ppm based on theweight of the precursor of monomer residue (a) in the molten reactionmixture.
 9. The method of claim 2, wherein the antioxidant is ahydroxycarboxylic acid and is selected from the group consisting oftartaric acid, maleic acid, lactic acid, tartronic acid and esters ofthese acids.
 10. The method of claim 2, wherein the antioxidant is ahydroxycarboxylic acid is selected from the group consisting of thesalts of tartaric acid, salts of maleic acid, salts of lactic acid, andsalts of tartronic acid.
 11. The method of claim 2, wherein theantioxidant is introduced to the reaction mixture prior to theintroduction of the polymerization catalyst.
 12. The method of claim 1,wherein monomer residue (a) has the structure,

where each R¹⁰ is independently at each occurrence a hydrogen atom,halogen atom, nitro group, cyano group , C₁-C₂₀ alkyl, C₄-C₂₀ cycloalkylradical, C₄-C₂₀ aryl radical, and n is an integer from 0 to
 4. 13. Themethod of claim 12, wherein monomer residue (a) is catechol, resorcinol,hydroquinone, butyl hydroquinone, methyl hydroquinone or any combinationthereof.
 14. The method of claim 12, wherein the antioxidant isintroduced to the reaction mixture prior to melting, during melting, orafter melting monomer residues (a), monomer residues (b), the carbonatesource or combinations thereof.
 15. The method of claim 12, wherein theantioxidant is introduced to the reaction mixture prior to meltingmonomer residues (a), monomer residues (b), or the carbonate sourcewherein the introduction of the antioxidant occurs in a melter or a feedline to a melter.
 16. The method of claim 12, wherein the antioxidant isintroduced to the reaction mixture after melting monomer residues (a),monomer residues (b), and the carbonate source wherein the introductionof the antioxidant to the molten reaction mixture occurs in a melter, afeed line to a monomer mix tank, the monomer mix tank, a feed line fromthe monomer mix tank to a first process unit, the first process unit, afeed line to a second process unit, the second process unit, a feed lineto a third process unit, the third process unit, or combinationsthereof.
 17. The method of claim 12, wherein the wherein the antioxidantis introduced to the reaction mixture during the melting of monomerresidues (a), monomer residues (b), or the carbonate source wherein theintroduction of the antioxidant occurs in a melter or a feed line to amelter.
 18. The method of claim 12, wherein the antioxidant isintroduced in an amount of less than 10 ppm based on the weight of theprecursor of monomer residue (a) in the reaction mixture.
 19. The methodof claim 12, wherein the antioxidant is introduced in an amount of lessthan 5 ppm based on the weight of the precursor of monomer residue (a)in the reaction mixture.
 20. The method of claim 19, wherein theantioxidant is introduced in an amount of less than 1 ppm based on theweight of the precursor of monomer residue (a) in the molten reactionmixture.
 21. The method of claim 12, wherein the antioxidant is ahydroxycarboxylic acid and is selected from the group consisting oftartaric acid, maleic acid, lactic acid, tartronic acid and esters ofthese acids.
 22. The method of claim 12, wherein the antioxidant is ahydroxycarboxylic acid is selected from the group consisting of thesalts of tartaric acid, salts of maleic acid, salts of lactic acid, andsalts of tartronic acid.
 23. The method of claim 12, wherein theantioxidant is introduced to the reaction mixture prior to theintroduction of the polymerization catalyst.
 24. The method of claim 1,wherein monomer residue (b) is BPA.
 25. The method of claim 24, whereinthe antioxidant is introduced to the reaction mixture prior to melting,during melting, or after melting monomer residues (a), monomer residues(b), the carbonate source or combinations thereof.
 26. The method ofclaim 25, wherein the antioxidant is introduced to the reaction mixtureprior to melting monomer residues (a), monomer residues (b), or thecarbonate source wherein the introduction of the antioxidant occurs in amelter or a feed line to a melter.
 27. The method of claim 25, whereinthe antioxidant is introduced to the reaction mixture after meltingmonomer residues (a), monomer residues (b), and the carbonate sourcewherein the introduction of the antioxidant to the molten reactionmixture occurs in a melter, a feed line to a monomer mix tank, themonomer mix tank, a feed line from the monomer mix tank to a firstprocess unit, the first process unit, a feed line to a second processunit, the second process unit, a feed line to a third process unit, thethird process unit, or combinations thereof.
 28. The method of claim 25,wherein the wherein the antioxidant is introduced to the reactionmixture during the melting of monomer residues (a), monomer residues(b), or the carbonate source wherein the introduction of the antioxidantoccurs in a melter or a feed line to a melter.
 29. The method of claim25, wherein the antioxidant is introduced in an amount of less than 10ppm based on the weight of the precursor of monomer residue (a) in thereaction mixture.
 30. The method of claim 25, wherein the antioxidant isintroduced in an amount of less than 5 ppm based on the weight of theprecursor of monomer residue (a) in the reaction mixture.
 31. The methodof claim 30, wherein the antioxidant is introduced in an amount of lessthan 1 ppm based on the weight of the precursor of monomer residue (a)in the molten reaction mixture.
 32. The method of claim 25, wherein theantioxidant is a hydroxycarboxylic acid and is selected from the groupconsisting of tartaric acid, maleic acid, lactic acid, tartronic acidand esters of these acids.
 33. The method of claim 25, wherein theantioxidant is a hydroxycarboxylic acid is selected from the groupconsisting of the salts of tartaric acid, salts of maleic acid, salts oflactic acid, and salts of tartronic acid.
 34. The method of claim 25,wherein the antioxidant is introduced to the reaction mixture prior tothe introduction of the polymerization catalyst.
 35. The method of claim1, wherein the carbonate source is diphenyl carbonate.
 36. The method ofclaim 1, wherein the carbonate source is an activated carbonate.
 37. Themethod of claim 36, wherein the activated carbonate isbismethylsalicylcarbonate.
 38. The method of claim 1, wherein up to 50mole % of the precursor of the carbonate source is derived from thegroup consisting of dicarboxylic acids, dicarboxylic acid esters,dicarboxylic acid halide or any combination thereof.
 39. The method ofclaim 1, wherein the inorganic catalyst is NaOH and the organic catalystis selected from the group consisting of TMAH, TBPA, and combinationsthereof.
 40. The method of claim 1, wherein the method further comprisesthe step of introducing a dihydric phenol to the reaction mixture withinthe series of process units through late monomer addition.
 41. Themethod of claim 40, wherein the antioxidant is introduced to thereaction mixture within the series of process units prior to theaddition of dihydric phenol through late monomer addition.
 42. Themethod of claim 1, wherein the copolymer has a molecular weight Mwbetween 10,000 and 100,000 g/mole (Polystyrene standards).
 43. Themethod of claim 42, wherein the copolymer has a molecular weight Mwbetween 25,000 and 40,000 g/mole (Polystyrene standards).
 44. The methodof claim 1, wherein the copolymer has a molecular weight Mw of at least10,000 g/mole (Polystyrene standards) and the molecular weight Mw issubsequently increased to a value higher than 25,000 g/mole (Polystyrenestandards) using a standard extrusion step.
 45. The method of claim 1,wherein the copolymer has a molecular weight Mw of at least 10,000g/mole (Polystyrene standards) and the molecular weight Mw issubsequently increased to a value higher than 25,000 g/mole (Polystyrenestandards) by further reaction of oligomers by means of solid statepolymerization.
 46. The method of claim 1, wherein the copolymer has anend cap level of at least 80%.
 47. The method of claim 46, wherein thecopolymer has an end cap level of at least 90%.
 48. A molded articleformed from copolycarbonate with improved color prepared by the methodcomprising the steps of: i. preparing a molten reaction mixturecomprising a first dihydroxy aromatic compound comprising monomerresidue (a), a second dihydroxy aromatic compound comprising monomerresidue (b), a carbonate source, and a polymerization catalyst, whereinmonomer residue (a) is a quinone structure or a structure capable offorming a quinone structure upon oxidation, wherein monomer residue (b)is a quinone structure or a structure capable of forming a quinonestructure upon oxidation different from monomer residue (a), or is,

where B is

—O—, —CO—, —S—, —SO₂—, a C₆-C₂₀ aromatic radical, or a C₆-C₂₀cycloaliphatic radical; the groups R¹ and R² are independently ahydrogen atom, C₁-C₂₀ alkyl radical, C₄-C₂₀ cycloalkyl radical, orC₄-C₂₀ aryl radical; or R¹ and R² together form a C₄-C₂₀ cycloaliphaticring which is optionally substituted by one or more C₁-C₂₀ alkyl, C₆-C₂₀aryl, C₅-C₂₁ aralkyl, C₅-C₂₀ cycloalkyl groups or a combination thereof,R³ is a divalent hydrocarbylene group, and R⁴ and R⁵ are independently ahydrogen atom, halogen atom, nitro group, cyano group, C₁- C₂₀ alkylradical C₄-C₂₀ cycloalkyl radical, or C₆-C₂₀ aryl radical and p and qare both integers from 0 to 4, ii. introducing an antioxidant such as ahydroxycarboxylic acid to the reaction mixture in an amount sufficientto result in a product copolycarbonate with improved color, iii.introducing the reaction mixture to a series of process units, iv.allowing the reaction mixture to polymerize thereby formingcopolycarbonate, wherein the copolycarbonate has improved color ascompared to a copolycarbonate formed in a melt process without theintroduction of antioxidant, and v. forming a molded article from thecopolycarbonate.
 49. A method for making a molded article formed fromcopolycarbonate with improved color prepared by the method comprisingthe steps of: i. preparing a molten reaction mixture comprising a firstdihydroxy aromatic compound comprising monomer residue (a), a seconddihydroxy aromatic compound comprising monomer residue (b), a carbonatesource, and a polymerization catalyst, wherein monomer residue (a) is aquinone structure or a structure capable of forming a quinone structureupon oxidation, wherein monomer residue (b) is a quinone structure or astructure capable of forming a quinone structure upon oxidationdifferent from monomer residue (a), or is,

where B is

—O—, —CO—, —S—, —SO₂—, a C₆-C₂₀ aromatic radical, or a C₆-C₂₀cycloaliphatic radical; the groups R¹ and R² are independently ahydrogen atom, C₁-C₂₀ alkyl radical, C₄-C₂₀ cycloalkyl radical, orC₄-C₂₀ aryl radical; or R¹ and R² together form a C₄-C₂₀ cycloaliphaticring which is optionally substituted by one or more C₁-C₂₀ alkyl, C₆-C₂₀aryl, C₅-C₂₁ aralkyl, C₅-C₂₀ cycloalkyl groups or a combination thereof,R³is a divalent hydrocarbylene group, and R⁴ and R⁵ are independently ahydrogen atom, halogen atom, nitro group, cyano group, C₁-C₂₀ alkylradical C₄-C₂₀ cycloalkyl radical, or C₆-C₂₀ aryl radical and p and qare both integers from 0 to 4, ii. introducing an antioxidant such as ahydroxycarboxylic acid to the reaction mixture in an amount sufficientto result in a product copolycarbonate with improved color, iii.introducing the reaction mixture to a series of process units, iv.allowing the reaction mixture to polymerize thereby formingcopolycarbonate, wherein the copolycarbonate has improved color ascompared to a copolycarbonate formed in a melt process without theintroduction of antioxidant, and v. forming a molded article from thecopolycarbonate.
 50. The method of claim 49, wherein the polymerizationcatalyst is introduced to the reaction mixture according to a selectedstrategy, wherein the strategy is selected from the group consistingof,
 1. introducing a polymerization catalyst to the molten reactionmixture after monomer residues (a), monomer residues (b), and carbonatesource are melted and prior to substantial polymerization, 2.introducing a polymerization catalyst to the reaction mixture or monomerresidues prior to melting with the proviso that residence time of theprocess from the start of melting until substantial polymerization hasoccurred is less than 4 hours, and
 3. or a combination thereof, whereinthe polymerization catalyst is an inorganic catalyst, an organiccatalyst, or both inorganic and organic catalyst which may be introducedseparately or together.
 51. The method of claim 48, wherein thepolymerization catalyst is introduced to the reaction mixture accordingto a selected strategy, wherein the strategy is selected from the groupconsisting of,
 1. introducing a polymerization catalyst to the moltenreaction mixture after monomer residues (a), monomer residues (b), andcarbonate source are melted and prior to substantial polymerization, 2.introducing a polymerization catalyst to the reaction mixture or monomerresidues prior to melting with the proviso that residence time of theprocess from the start of melting until substantial polymerization hasoccurred is less than 4 hours, and
 3. or a combination thereof, whereinthe polymerization catalyst is an inorganic catalyst, an organiccatalyst, or both inorganic and organic catalyst which may be introducedseparately or together.
 52. The method of claim 1, wherein thepolymerization catalyst is introduced to the reaction mixture accordingto a selected strategy, wherein the strategy is selected from the groupconsisting of,
 1. introducing a polymerization catalyst to the moltenreaction mixture after monomer residues (a), monomer residues (b), andcarbonate source are melted and prior to substantial polymerization, 2.introducing a polymerization catalyst to the reaction mixture or monomerresidues prior to melting with the proviso that residence time of theprocess from the start of melting until substantial polymerization hasoccurred is less than 4 hours, and
 3. or a combination thereof, whereinthe polymerization catalyst is an inorganic catalyst, an organiccatalyst, or both inorganic and organic catalyst which may be introducedseparately or together.